Prior art tensioners typically apply hydraulic forces to tension a stud. Prior art hydraulic tensioners typically involve the use of a nut which must be positioned on the stud while hydraulic pressure is applied. In many applications using a remotely operated vehicle (“ROV”), it is inconvenient to use a tensioner which requires simultaneous positioning of the stud and application of hydraulic pressure.
Prior art tensioners comprising hydraulic nuts require an extra operation to hold the stretched stud. For subsea applications where remotely controlled ROV manipulator arms are used to tension such nuts, this extra operation increases the difficulty of using such tensioners.
The present invention provides a self locking tensioner, which may be tensioned using hydraulic pressure, and which has greater position setting flexibility than do prior art hydraulic tensioners. In another embodiment, the present invention provides a tensioner comprising a fluid operated nut that will automatically hold whatever position the nut is stretched to without an extra operation, as discussed above.
In one preferred embodiment, the present invention provides for tensioning or detensioning of a piston or stud in whatever increment of tensioning or detensioning is desired. The term “detensioning” as used herein, means movement of a tensioned member to reduce the magnitude of tensile force on the member.